YANGON, Feb 28 (Reuters) - Myanmar has ordered Medecins Sans Frontieres (MSF) to halt all its work in the country, leaving tens of thousands of people without vital care, the medical aid group said on Friday.

MSF did not give a reason for the suspension, but local media reported government officials had been angered by the charity's public comments on the western strife-torn state of Rakhine.

The Nobel Prize-winning aid group has been giving care there to both ethnic Rakhine Buddhists and Rohingya Muslims, a mostly stateless minority who live in apartheid-like conditions and who otherwise have little access to healthcare.

The United Nations and human rights groups say at least 40 Rohingya were killed by security forces and ethnic Rakhine Buddhist civilians in a restricted area of the state in January.

Myanmar's government denies that any massacre took place. Government spokesman Ye Htut accused MSF, in comments to local media on Friday, of falsely reporting that it had treated victims near the scene of the alleged mass killing.

If confirmed, the massacre would take to at least 277 the number of people killed in religious conflict across Myanmar since June 2012. More than 140,000 people have been displaced.

Ye Htut and other government officials were unavailable for comment on Friday.

"INTERNAL AFFAIR"

MSF said it was shocked by the decision to suspend its work and "extremely concerned about the fate of tens of thousands of patients currently under our care across the country," it a statement out if its Amsterdam office.

It said it had to close clinics serving 30,000 HIV/AIDS patients, and more than 3,000 people with tuberculosis would not be able to get vital medicine.

"MSF's actions are guided by medical ethics and the principles of neutrality and impartiality. MSF is in discussions with the Government of Myanmar to allow our staff to resume life-saving medical activities across the country and continuing addressing the unmet heath needs of its people," the statement read.

The U.S. embassy in Myanmar had earlier urged the government to give aid agencies "unfettered access" after initial reports emerged that MSF had been barred from Rakhine.

Reports of incidents in Rakhine are difficult to verify independently as large parts are off limits to journalists. The government also controls access by international aid groups, despite a wave of democratic reforms since military rule ended in 2011.

Myanmar's government has repeatedly rejected reports by MSF, the United Nations and human rights groups that Rohingya villagers in Maungdaw township were attacked and their homes looted.

On Jan. 29, the government called diplomats to a briefing where officials said they had found no evidence of a massacre but promised further investigation.

A request by U.S. Ambassador Derek Mitchell to include an international representative on the investigating team was denied by Foreign Minister Wunna Maung Lwin, who said it was "an internal affair". (Additional reporting by Thin Lei Win in Bangkok; Writing by Alan Raybould; Editing by Robert Birsel and Andrew Heavens)

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